EP3872503B1 - Monitoring device and method for monitoring the insulation of an unshielded electrical system with grounded liquid cooling - Google Patents

Description

The invention relates to a monitoring device for monitoring an insulation resistance for an ungrounded electrical system, which has a liquid cooling system that is grounded with a coolant and has a feed line and a return line, with the feed line and the return line each being designed as an electrically conductive pipeline section connected to ground potential which is connected to the electrical system by an electrically insulated pipeline section with the pipeline length li.

In the case of increased requirements for operational, fire and contact safety, the network form of an unearthed electrical system is used, which is also referred to as an isolated system (French: Isole Terre - IT) or IT system. In this type of system, all active parts are isolated from the earth potential - with respect to earth. The advantage of such an unearthed electrical system is that the function of the electrical system is not impaired in the event of an insulation fault, since there is no closed impedance between the electrical system and ground due to the ideally infinitely large impedance value Circuit can form. However, the resistance of the unearthed electrical system to ground (insulation resistance) must be constantly monitored, since if another fault occurs, a fault loop could possibly arise and the fault current flowing in connection with an overcurrent protection device would result in the electrical system being switched off with operational standstill.

According to the state of the art, insulation monitoring is carried out with an insulation monitoring device which is connected between an active conductor of the electrical system and earth, superimposes a measurement voltage as a measurement signal on the electrical system to be monitored and evaluates a fault current flowing through the insulation resistance to determine the insulation resistance.

If the electrical systems to be monitored include power electronics, as is the case, for example, in numerous power converter applications with their power semiconductors, the heat generated in the electrical system is effectively dissipated via a liquid cooling system. Demineralized water is preferably used as the cooling liquid. The coolant circulation pump and the coolant conditioner are mainly fed from a power supply system with a grounded network form (grounded power supply system) and are therefore connected to ground potential. In most cases there is also a direct connection between the coolant system and the grounded drinking water pipe system in order to be able to quickly compensate for a loss of coolant.

In order to be able to operate the electrical system that requires cooling, for example a converter, ungrounded and at the same time to be able to supply the liquid cooling system with a grounded power supply system, it is known to electrically separate the grounded cooling system from the ungrounded electrical system by means of electrically insulated coolant pipes or pipe sections.

However, there is no complete galvanic isolation between the ungrounded electrical system and the grounded liquid cooling system due to the practically always present and process-related fluctuating electrolytic conductivity of the cooling liquid. This incomplete electrical isolation between the otherwise isolated ungrounded electrical system and the grounded operated liquid cooling can be modeled by a coolant resistance R _K .

1 shows the problem on which the invention is based. An ungrounded electrical system 2, represented here by way of example by a power converter with liquid-cooled power electronics, is connected to a liquid cooling system that is operated with grounding. The liquid cooling system includes a coolant drive 4, which is connected to the electrical system 2 to be cooled via a supply line 6 and a return line 8, in which the coolant 3 flows. Both the supply line 6 and the return line 8 each consist of an electrically conductive pipe section 10 which is connected to the ground potential PE. In the direction of the electrical system 2 , an electrically insulated pipeline section 12 adjoins the electrically conductive pipeline section 10 —in each case for the supply line 6 and the return line 8 —which opens out into the electrical system 2 .

In order to monitor the insulation resistance _Rf of the electrical system 2, the electrical system 2 is equipped with an insulation monitoring device 14 in accordance with the regulations.

The electrolytic conductivity of the coolant is represented by the coolant resistance R _K as a lumped element and is parallel to the insulation resistance R _f . If the coolant resistance R _K assumes an inadmissibly small value in comparison to the insulation resistance Rf when the conductivity of the coolant 3 is too high, standard-compliant monitoring of the electrical system 2 with the insulation monitoring device 14 is no longer reliably possible. Is the coolant resistance R _K with quite normal values of a few kΩ in parallel with a (system) insulation resistance R _f that has a high insulation level, _e.g issue an alarm to meet the normative requirements.

From these considerations, it becomes clear that standard-compliant monitoring is not possible.

This problem is exacerbated when several ungrounded electrical subsystems 16, for example several powerful power converters, are fed from a common ungrounded transformer 15 for reasons of cost.

2 shows such a constellation, in which, for example, three ungrounded electrical subsystems 16 are fed from a common transformer 15. Provided that the geometry of the coolant supply and the electrolytic conductivity of the coolant 3 are the same in all three electrical subsystems 16, the total coolant resistance results in approximately one third of the value of the coolant resistance R _K 1 . The resulting systematic error when determining the insulation resistance Rf with an insulation monitoring device 14 is unacceptably large.

To solve the problem, according to the state of the art, constructive measures can be taken during system planning to ensure that the coolant resistance is large enough to keep the systematic error in insulation monitoring small in accordance with the normative requirements. Known measures are, for example, a corresponding design of the geometry of the coolant supply, the use of very high-quality materials in order to keep corrosion and/or migration effects low when using coolants with very low conductance values.

However, these constructive measures lead to significantly increased system costs, so that in practice the response values of the insulation monitoring device for the pre- and main alarm are set to a very low-impedance level, which deviates significantly from the normative recommendations. In terms of measuring technology, the insulation monitoring devices in this environment often work in a borderline area and outside of their technical specifications. For the user, this also means an increase in false alarms. The state of the art can be found, for example, in the documents DE102016009346 , US2009096464 and JP2010164531 .

The present invention is therefore based on the object of proposing a monitoring device and a method for monitoring the insulation resistance for an ungrounded electrical system which is operated with a grounded liquid cooling system, which enable reliable and cost-efficient monitoring of the insulation resistance.

This object is achieved by the characterizing features of claim 1 in relation to a device.

The basic idea of the invention is that a measuring signal for determining the insulation resistance is fed in serially via the coolant resistance. In contrast to the prior art, in which the measurement signal is coupled to an active conductor to ground parallel to the coolant resistance R _K , in the constellation according to the invention the coolant resistance R _K is not parallel to the insulation resistance Rf to be determined, but is related to it connected in series. This eliminates the systematic error described above.

The monitoring device therefore has one or two low-impedance measurement signal sources, which each generate a measurement signal in the form of a measurement voltage, depending on the type of coupling of the measurement signal - a joint coupling via the supply line and the return line or a one-sided coupling only into the supply line or into the return line . The measuring signal source(s) is/are in contact with the electrically conductive pipeline section or generally with the earth potential via an earth potential connection.

In order to couple in the measurement signal, a coupling connection of the measurement signal source is connected to a conductive coupling-in tube element that makes contact with the coolant.

In order to measure a coupling current, which flows in the coolant flowing through the electrically insulated pipeline section, a coupling current measuring sensor is arranged on the electrically insulated pipeline section.

A fault current measuring sensor is connected downstream of the coupling current measuring sensor in the direction of the electrical system. This is used to measure a fault current, which is also formed in the coolant flowing through the electrically insulated pipeline section and is used to determine the insulation resistance.

On the electrically insulated pipeline section, the (one-piece) coupling pipe element between the coupling current measuring sensor on the ground potential side and the fault current measuring sensor on the system side is arranged in such a way - or in the case of two-piece coupling, both coupling pipe elements are arranged in such a way - that the pipe length of the electrically insulated Pipe section is divided into a coupling length extending between the electrically conductive pipe section and the coupling-in pipe element and a resistance length extending from the coupling-in pipe element to the electrical system.

The monitoring device has to calculate the insulation resistance from the measured voltage, the detected coupling current, the detected error current, the coupling length and the resistance length a computing unit, for example in the form of a microprocessor.

Based on the coolant drive fed by a grounded power supply system and electrically conductive pipe sections connected to it, the order in which the elements of coupling current measuring sensor, coupling pipe element and residual current measuring sensor are arranged is always the same, the design for attaching these elements to the supply line or return line can however differ.

In one possible embodiment, the residual current measuring sensor has a residual current measuring current transformer, which together encloses the supply line and the return line. The coupling current measuring sensor also has a coupling current measuring current transformer, which together encloses the supply line and the return line.

The coupling tube element is either made in one piece and connected to the measurement signal source, so that the measurement signal is coupled synchronously in common mode into the supply line and the return line, or the coupling tube element is made in two parts and consists of a supply line coupling tube element and a return line launch element. The latter two elements are each connected to one of the measurement signal sources and synchronously couple the respective measurement signals on one side into the supply line and the return line in common mode. The measurement signal is therefore always coupled into the supply line and the return line.

The residual current measuring sensor has a residual current measuring current transformer and the coupling current measuring sensor has a coupling current measuring current transformer, the residual current measuring current transformer and the coupling current measuring current transformer both comprising the supply line on one side or both comprising the return line on one side.

The use of the monitoring device according to the invention for monitoring the insulation resistance for an electrical system which is an ungrounded converter system is particularly advantageous.

In particular, powerful power converter systems (alternating, rectifying and converter systems), which require a high cooling capacity, can be reliably checked with regard to the insulation resistance using the monitoring device according to the invention.

A remaining measurement uncertainty in the galvanically isolated current measurement via the fault current measuring sensor and the coupling current measuring sensor can be reduced by determining a measuring current via the voltage drop across a load resistor in the measuring voltage source. This consideration results in an approach according to the invention which is an alternative to the current measurement and uses a voltage measurement, which, however, requires known and stable geometry conditions of the coolant supply.

The object on which the invention is based is thus further achieved by a monitoring device according to the features of claim 5.

In this embodiment, too, the monitoring device has a low-impedance measurement signal source for generating a measurement signal with a measurement voltage. The measurement signal source includes a ground potential connection, which is connected to the electrically conductive pipeline section, and a coupling connection. A conductive coupling pipe element, which contacts the coolant, is connected to this coupling connection of the measurement signal source and synchronously couples the measurement signal into the supply line and the return line in common mode.

In contrast to the monitoring device described in claim 1, this embodiment of the monitoring device does not have a current measurement, but instead comprises a voltmeter and a conductive, coolant-contacting voltage measuring tube element for measuring a partial voltage on the electrically insulated pipeline section.

A first voltage measurement input of the voltmeter is connected to the coupling connection of the measurement signal source, a second voltage measurement input of the voltmeter is connected to the voltage measurement tube element for detecting the partial voltage.

The coupling pipe element is arranged on the electrically insulated pipe sections in such a way that there is a certain coupling length on the electrically insulated pipe sections between the system-side end of the electrically conductive pipe sections arranged on the ground potential side and the coupling pipe element. Then, in the direction of the electrical system, the voltage-measuring tube element is arranged on the electrically insulated pipeline sections in such a way that a distance with a defined voltage-measuring length is established between the coupling-in tube element and the voltage-measuring tube element. There is a defined resistance length on the electrically insulated pipe sections between the voltage measuring tube element and the electrical system.

The monitoring device in this embodiment with voltage measurement also has a computing unit that is designed to calculate the insulation resistance from the measurement voltage, the measurement signal, an input measurement current, the partial voltage, the coupling length, the voltage measurement length and the resistance length.

It is advantageous to use the monitoring device to monitor the insulation resistance for an ungrounded power converter system as an electrical system in order to meet the cooling requirements, particularly in the case of high-performance power converter systems.

Based on the monitoring device with current measurement (claim 1) and the design of the monitoring device with voltage measurement (claim 5), an extended monitoring device for monitoring a common insulation resistance of several ungrounded electrical subsystems fed by a common transformer is designed.

The respective electrical subsystems, including the common transformer, correspond to the above-mentioned ungrounded electrical system, which in each case has a liquid cooling system that is grounded with a coolant and has a supply line and a return line.

According to the invention, at least two of the unearthed electrical subsystems in the extended monitoring device are equipped with a monitoring device according to one of Claims 1 to 6.

The expanded monitoring device also has a synchronization control device for synchronously coupling the measurement signals into the respective electrical subsystems to be monitored.

This ensures that the measurement signals generated by the measurement signal sources and fed into the respective subsystem are synchronous in time.

The synchronization control device advantageously has an amplitude control device for controlling the measurement signal amplitudes of the measurement signals generated in the respective monitoring devices.

The control of the measurement signal amplitudes in the respective monitoring devices assigned to the electrical subsystems is not absolutely necessary, but can be used in the case of very unequal geometric distribution of the coolant supply to adjust any leakage currents to earth or residual voltages to earth for each electrical subsystem as equally as possible. This avoids an unequal current and voltage load on individual electrical subsystems, because an extreme deviation in the leakage currents in the individual electrical subsystems can lead to an additional systematic measurement error due to the respective measurement signal sources and/or current sensors entering an unfavorable working range.

Advantageously, the amplitude control device can be used to control the measurement signal amplitude for each electrical subsystem to be monitored, so that the overall operational measurement reliability of the insulation monitoring system is largely independent of expected process-related fluctuations in parameters of the coolant system (e.g. fluctuation in electrolytic conductivity) and the expected differences in the geometric design of the coolant circuit (e.g. different lengths of the coolant pipes).

The embodiments of the monitoring devices according to the invention described above are based on the technical teachings described in the independent method claims 9 , 11 and 13 . In this respect, the aforementioned technical effects and the resulting advantages also apply to the features listed in the method claims.

In particular, existing coupling options in liquid-cooled power converter applications due to the design of the coolant supply can be used in an advantageous manner, thereby optimizing measurement technology by avoiding a coolant resistance to ground that is parallel to the insulation resistance.

Advantageously, the power converted in an insulation monitoring device and its voltage load can also be reduced in medium-voltage applications.

Further advantageous design features result from the following description and the drawings, which explain preferred embodiments of the invention using examples.

Fig. 1

Ein ungeerdetes elektrisches System mit geerdet betriebener Flüssigkeitskühlung;

Fig. 2

von einem gemeinsamen Transformator gespeiste ungeerdete elektrische Subsysteme;

Fig. 3

eine erfindungsgemäße Überwachungsvorrichtung mit gemeinsamer Strommessung und einteiliger Messsignaleinkopplung;

Fig. 4

eine erfindungsgemäße Überwachungsvorrichtung mit einseitiger Strommessung und einteiliger Messsignaleinkopplung;

Fig. 5

eine erfindungsgemäße Überwachungsvorrichtung mit gemeinsamer Strommessung und zweiteiliger Messsignaleinkopplung;

Fig. 6

ein Ersatzschaltbild zur Bestimmung des Isolationswiderstands nach Fig. 3;

Fig. 7

eine erfindungsgemäße Überwachungsvorrichtung mit Spannungsmessung;

Fig. 8

ein Ersatzschaltbild zur Bestimmung des Isolationswiderstands nach Fig. 7;

Fig. 9

eine erfindungsgemäße erweiterte Überwachungsvorrichtung mit Strommessung;

Fig. 10

ein Ersatzschaltbild zur Bestimmung des Isolationswiderstands nach Fig. 9;

Fig. 11

eine erweiterte Überwachungsvorrichtung mit Spannungsmessung;

Fig. 12

ein Ersatzschaltbild zur Bestimmung des Isolationswiderstands nach Fig. 11.

Show it:

1

An ungrounded electrical system with grounded powered liquid cooling;

2

unearthed electrical subsystems fed from a common transformer;

3

a monitoring device according to the invention with common current measurement and one-piece measurement signal coupling;

4

a monitoring device according to the invention with one-sided current measurement and one-piece measurement signal coupling;

figure 5

a monitoring device according to the invention with common current measurement and two-part measurement signal coupling;

6

an equivalent circuit diagram for determining the insulation resistance 3 ;

7

a monitoring device according to the invention with voltage measurement;

8

an equivalent circuit diagram for determining the insulation resistance 7 ;

9

an extended monitoring device with current measurement according to the invention;

10

an equivalent circuit diagram for determining the insulation resistance 9 ;

11

an advanced monitoring device with voltage measurement;

12

an equivalent circuit diagram for determining the insulation resistance 11 .

1 1 shows an ungrounded electrical system 2 to illustrate the problem, which has a liquid cooling system operated with a coolant 3 grounded and having a feed line 6 and a return line 8 .

An electrically conductive pipe section 10 is arranged on a coolant drive 4 (ground potential side) connected to the ground potential PE for the feed line 6 and the return line 8 of the coolant 3, to which (on the system side) an electrically insulated pipe section 12 is connected, which is connected to the ungrounded electrical System 2 opens.

In order to determine the insulation resistance _Rf of the electrical system 2 between one or more active conductors to earth PE, according to the prior art an insulation monitoring device 14 is connected between the unearthed electrical system 2 and earth PE.

As a result of the electrolytic conductivity of the coolant 3, the electrical system 2 is not completely electrically isolated from ground PE. There is therefore an electrically conductive connection to earth PE, which is modeled here by the coolant resistance R _K as a lumped element. This coolant resistance R _K is parallel to that determined insulation resistance R _f and has a significant influence on the measurement of the insulation resistance.

2 shows the arrangement of three electrical subsystems 16 which are fed from a common transformer 15. As a result of the parallel connection of the electrical subsystems 16, the total coolant resistance is reduced to approximately one-third and thus leads to an even more imprecise determination of the insulation resistance Rf.

3 shows a monitoring device 100 according to the invention with a common current measurement and one-piece measurement signal coupling in the application for one in the 1 illustrated ungrounded electrical system 2 with grounded operated liquid cooling.

A coupling current measuring sensor 40 is arranged on the ground potential side of the electrically insulated pipeline section 12 with the pipeline length l _i , whose coupling current measuring current transformer jointly encloses the supply line 6 and the return line 8 . The coupling current measuring sensor 40 detects a coupling current I _AK which flows in the coolant 3 flowing through the electrically insulated pipeline section 12 .

Downstream from the coupling current measuring sensor 40 in the direction of the electrical system 2 is a fault current measuring sensor 42, which also encloses the feed line 6 and the return line 8 together and which detects a fault current I _Ri which - in the illustration "above" the measurement signal coupling - in the coolant 3 flowing through the electrically insulated pipeline section 12 .

Between the coupling current measuring sensor 40 and the residual current measuring sensor 42, at a distance of a coupling length l _AK - measured from the (system-side end of) the electrically conductive pipeline section 10 - a one-piece coupling tubular element 50 is attached in the electrically insulated pipeline section 12. Of the Coupling pipe element 50 until the electrically insulated pipe section 12 is connected to the electrical system 2, a resistance length l _Ri remains, which together with the coupling length l _AK results in the pipe length li of the electrically insulated pipe section 12.

In order to feed in a measurement signal (measurement voltage U _m ), the one-piece coupling tubular element 50 is connected to a measurement voltage source 30 via a coupling connection 32 . A ground potential connection 31 of the measurement signal source 30 is at ground potential PE, for example connected to the electrically conductive pipeline section 10.

In order to calculate the insulation resistance Rf, the monitoring device 100 has an arithmetic unit 60 which evaluates the output signals of the coupling current measuring sensor 40 , the residual current measuring sensor 42 and the measuring signal source 30 .

4 shows an embodiment of the monitoring device 101 according to the invention with one-sided current measurement and one-piece measurement signal coupling.

In contrast to the in 3 In the embodiment shown, the coupling current measuring sensor 40 and the error current measuring sensor 42 are designed on one side, ie both measuring current transformers are arranged either on one side around the feed line 6 or both on one side around the return line 8 .

The monitoring device 101 has in the same way as in 3 The monitoring device 100 shown in FIG 4 arithmetic unit 60, not shown.

figure 5 shows a further embodiment of the monitoring device 102 with common current measurement and two-part measurement signal coupling.

The current is measured as in the in 3 The monitoring device 100 shown has a coupling current measuring sensor 40 arranged on the ground potential side and a residual current measuring sensor 42 arranged on the system side, each of which encloses the supply line 6 and the return line 8 together.

However, the coupling pipe element 50 is divided in two parts into a supply pipe element 52 and a return pipe element 54 . The feed line coupling-in tubular element 52 and the return line coupling-in tubular element 54 are each connected to a measurement signal source 30, the respective measurement signals being synchronously coupled into the feed line 6 and the return line 8 on one side in common mode.

If the measurement signal were not coupled synchronously in common mode to ground in the feed line 6 and the return line 8, for example only in the feed line 6, electrical leakage currents via the coolant return line would again be present as an electrical resistance parallel to the determining insulation resistance Rf. That would not solve the underlying problem.

In 6 is a from the monitoring device 100 after 3 derived electrical equivalent circuit diagram for determining the insulation resistance Rf is shown.

Ausgehend von einem konstanten Querschnitt der Kühlmittelzuführung und einer entlang der Kühlmittelzuführung konstanten elektrolytischen Leitfähigkeit des Kühlmittels 3 kann der Innenwiderstand Ri aus dem zuvor ermittelten Wert des Ankoppelwiderstands R_AK und dem Verhältnis der Widerstandslänge l_Ri zu der Ankopplungslänge l_AK in dem elektrisch isolierten Rohrleitungsabschnitt 12 wie folgt bestimmt werden $$R_i=R_{\mathit{AK}}\ast \frac{l_{\mathit{Ri}}}{l_{\mathit{AK}}}$$

the inside 1 The modeled coolant resistance R _K is represented here by a coupling resistance R _AK and an internal resistance Ri. The coupling resistance R _AK therefore results from the quotient of the amplitudes of the synchronously impressed measuring signal U _m and the coupling current I _AK measured by the coupling current measuring sensor 40 $$R_{\mathit{AK}}=\frac{u_m}{I_{\mathit{AK}}}.$$

Assuming a constant cross-section of the coolant supply and a constant electrolytic conductivity of the coolant 3 along the coolant supply, the internal resistance Ri can be calculated from the previously determined value of the coupling resistance R _AK and the ratio of the resistance length l _Ri to the coupling length l _AK in the electrically insulated pipeline section 12 as follows to be determined $$R_i=R_{\mathit{AK}}\ast \frac{l_{\mathit{Ri}}}{l_{\mathit{AK}}}$$

According to the invention, fluctuations in the electrolytic conductivity of the coolant 3 are recognized via the change in the internal resistance Ri and can be taken into account when determining the insulation resistance Rf. A systematic measurement error is thereby avoided.

It should be noted that in the electrical equivalent circuit diagram, the coolant 3 flowing in the supply line 6 and the return line 8 is shown in its electrical effect as a (single) resistance Ri or a (single) coupling resistance R _K .

Based on the electrical equivalent circuit diagram, the insulation resistance Rf can be determined as follows using the current divider rule $$R_f=\frac{u_m}{I_{\mathit{AK}}}\ast \left(\frac{I_{\mathit{AK}}}{I_{\mathit{Ri}}}-\frac{l_{\mathit{Ri}}}{l_{\mathit{AK}}}\right)$$

7 shows a monitoring device 103 according to the invention with a voltage measurement.

In this embodiment, the current measurement described in the above embodiments is replaced by a voltage measurement using a voltmeter 70 .

The measurement signal is coupled in, as in the above-mentioned embodiments, with a low-impedance measurement signal source 30 to which the Distance of a coupling length l _AK1 - measured from the system-side end of the electrically conductive pipe section 10 - a arranged on the electrically insulated pipe section 12 coupling pipe element 50 is connected.

To measure a partial voltage Ui, voltmeter 70 has a first voltage measuring input 72 connected to coupling connection 32 of measuring voltage source 30 and has a second voltage measuring input 74, which is connected to a conductive voltage measuring tube element 76 that contacts coolant 3.

The voltage-measuring tubular element 76 is attached downstream of the coupling tubular element 50 at a distance of a voltage length l _AK2 in the direction of the electrical system 2 . Starting from the voltage-measuring tube element 76, a resistance length l _Ri remains in the direction of the electrical system 2, which together with the coupling length l _AK1 and the voltage length l _AK2 results in the pipeline length l _i of the electrically insulated pipeline section 12.

The arithmetic unit 60 (not shown) determines the insulation resistance R _f from the detected values.

8 shows a from the monitoring device 103 after 7 Derived electrical equivalent circuit diagram for determining the insulation resistance R _f .

This in 6 The equivalent circuit diagram valid for the monitoring device 100 with current measurement was modified for the monitoring device 103 with voltage measurement. Connected in series with the coupling resistor R _AK1 is a measuring resistor R _AK2 , via which a partial voltage Ui existing on the electrically insulated pipeline section 12 is detected.

Since there is no current detection, the fault current I _Ri and the coupling current I _AK are initially unknown. In modification of the figure 5 The calculation formula given is based on the equivalent circuit diagram 8 the calculation of the insulation resistance as follows $$\mathit{RF}=\frac{\left(u_i+{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">K</figure-callout>}}_2\ast u_m\right)\ast \left({\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">K</figure-callout>}}_2\ast u_m-u_i\ast \left({\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">K</figure-callout>}}_2+K_i\right)\right)}{u_i\ast {\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">K</figure-callout>}}_2\ast I_m}\mathrm{With}{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">K</figure-callout>}}_{\mathrm{2}}=\frac{l_{\mathit{AK}2}}{l_{\mathit{AK}1}}\mathrm{and}{K}_i=\frac{l_{\mathit{Ri}}}{l_{\mathit{AK}1}}$$

9 shows an expanded monitoring device 110 according to the invention for three ungrounded electrical subsystems 16 fed by a common transformer 15.

Each of the subsystems 16 to be monitored is followed by a monitoring device 102 according to the invention figure 5 assigned. The monitoring device 102 after figure 5 was selected here as an example—in principle, any one of the claimed monitoring devices 100, 101, 102, 103 can be assigned to each subsystem 16 to be monitored.

The expanded monitoring device 110 has a synchronization control device 80, which enables the measurement signals to be coupled synchronously into the respective electrical subsystems 16 to be monitored.

In addition, an amplitude control device 82 is integrated into the synchronization control device 80 and controls the measurement signal amplitudes of the measurement signals generated in the respective monitoring devices 102 .

In addition, the processing unit arranged in the individual monitoring devices 102 can be replaced by a common higher-level processing unit 61 .

10 1 shows an electrical equivalent circuit diagram for determining the insulation resistance Rf with an extended monitoring device 110 9 .

Since the extended monitoring device 110 is suitable for an application of n (n≧2) electrical subsystems, the equivalent circuit diagram is generally valid for n electrical subsystems.

The equivalent circuit diagram also shows a functional group consisting of the synchronization control device 80 and the amplitude control device 82, which are connected to the respective measurement signal sources 30.

Based on the equation for the equivalent circuit diagram in figure 5 the calculation of a total insulation resistance value Rf in an arrangement consisting of n electrical subsystems 16 which is fed from a common transformer 15 can be determined as follows from the addition of the individual conductance values or as a parallel connection of the calculated individual insulation resistance values R _fi $$R_f=\frac{1}{{\displaystyle {\sum }_{i=1}^n\frac{1}{R_{\mathit{fi}}}}}$$

The individual insulation resistance values R _fi in the above formula are determined analogously to the equation 6 each to $$\begin{array}{ccc}{R}_{f1}=\frac{u_{m1}}{I_{\mathit{AK}1}}\ast \left(\frac{I_{\mathit{AK}1}}{I_{\mathit{Ri}1}}-\frac{l_{\mathit{Ri}1}}{l_{\mathit{AK}1}}\right)& {\mathrm{<figure-callout\; id="2"\; label="R\; f"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">R</figure-callout>}}_f=\frac{u_{m2}}{{\mathrm{<figure-callout\; id="2"\; label="I\; AK"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathit{AK}}}\ast \left(\frac{I_{\mathit{AK}2}}{{\mathrm{<figure-callout\; id="2"\; label="I\; Ri"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathit{Ri}}}-\frac{l_{\mathit{Ri}2}}{l_{\mathit{AK}2}}\right)& R_{\mathit{fn}}=\frac{u_{\mathit{mn}}}{I_{\mathit{AKn}}}\ast \left(\frac{I_{\mathit{AKn}}}{I_{\mathit{ring}}}-\frac{l_{\mathit{ring}}}{l_{\mathit{AKn}}}\right)\end{array}$$

11 shows an expanded monitoring device 111 for three commonly supplied electrical subsystems 16, each of these subsystems having a monitoring device 103 with voltage measurement according to the invention 7 Is provided.

The expanded monitoring device 111 has a synchronization control device 80 , a common computing unit 61 and optionally an amplitude control unit 82 .

12 FIG. 12 shows an electrical equivalent circuit diagram for the extended monitoring device with voltage measurement 11 .

In this embodiment too, the measurement voltage sources U _m of the individual electrical subsystems 16 must run synchronously with one another in order to prevent the measurement signals from interfering with one another. In an extreme case, for example, it is conceivable that the measurement current I m impressed by a measurement signal source 30 cancels out with the measurement current I _m impressed by another measurement signal source 30 . Optimum metrological operation is expected when the measurement signal amplitudes are set in such a way that the current through the insulation resistance Rf is approximately equally distributed among all measurement branches. The insulation resistance is calculated for each individual branch based on the known length ratios of the coolant supply, the known measuring voltage amplitudes U _m , the values for Ui measured for each measuring branch and the measured current I _m fed in in each case. The overall insulation value is then formed from the sum of the n individual values divided by n.

Claims (14)

1. A monitoring device (100, 101, 102) for monitoring an insulation resistance (R_f) for an ungrounded electric system (2) which comprises a liquid cooling which is operated to ground using a refrigerant (3) and has a supply line (6) and a return line (8), the supply line (6) and the return line (8) each being realized as a tube section (10) which is connected to a ground potential (PE) and is electrically conductive and to which an electrically insulated tube section (12) is connected which has a tube length (l_i) and is connected to the electric system (2),
   characterized by

   one or two low-impedance measuring signal sources (30) each configured for generating a measuring signal having a measuring voltage (U_m), each comprising a ground-potential connection (31) connected to the electrically conductive tube section (10), and each comprising a coupling connection (32),

   a coupling-current measuring sensor (40) for measuring a coupling current (I_AK) which flows in the refrigerant (3) flowing through the electrically insulated tube section (12),

   a fault-current measuring sensor (42) which is switched downstream of the coupling-current measuring sensor (40) in the direction of the electric system (2) and is configured for measuring a fault current (I_Ri) which flows in the refrigerant (3) flowing through the electrically insulated tube section (12),

   a conductive coupling tube element (50) which contacts the refrigerant (3) and is electrically connected to the coupling connection (32) of the measuring signal source (30) for coupling the measuring signal, the coupling tube element (50) being disposed in such a manner on the electrically insulated tube section (12) between the coupling-current measuring sensor (40) and the fault-current measuring sensor (42) that the tube length (l_i) of the electrically insulated tube section (12) is divided into a coupling length (I_AK) extending between the electrically conductive tube section (10) and the coupling tube element (50) and a resistance length (l_Ri) extending from the coupling tube element (50) to the electric system (2),

   a computing unit (60) which is configured for computing the insulation resistance (Rf) from the measuring voltage (U_m), the detected coupling current (I_AK), the detected fault current (I_Ri), the coupling length (I_AK) and the resistance length (l_Ri).
2. The monitoring device (100, 102) according to claim 1, characterized in that

   the fault-current measuring sensor (42) comprises a fault-current measuring current transformer which encircles both the supply line (6) and the return line (8), and

   the coupling-current measuring sensor (40) comprises a coupling-current measuring current transformer which encircles both the supply line (6) and the return line (8), and

   the coupling tube element (50) is realized in one part and is connected to the measuring signal source (30) and the measuring signal is synchronously coupled both into the supply line (6) and the return line (8) in common mode, or

   the coupling tube element (50) is divided into two parts in a supply-line coupling tube element (52) and a return-line coupling tube element (54) which are each connected to one of the measuring signal sources (30) and synchronously couple the corresponding measuring signals into the supply line (6) or the return line (8) on one side in common mode.
3. The monitoring device (101) according to claim 1,
   characterized in that

   the fault-current measuring sensor (42) comprises a fault-current measuring current transformer and

   the coupling-current measuring sensor (40) comprises a coupling-current measuring current transformer,

   the fault-current measuring current transformer and the coupling-current measuring current transformer both encircle the supply line (6) on one side and the return line (8) on one side, and

   the coupling tube element (50) is realized in one part and is connected to the measuring signal source (30) and the measuring signal is synchronously coupled together into the supply line (6) and the return line (8) in common mode, or

   the coupling tube element (50) is divided into two parts in a supply-line coupling tube element (52) and a return-line coupling tube element (54) which are each connected to one of the measuring signal sources (30) and synchronously couple the corresponding measuring signals into the supply line (6) or the return line (8) on one side in common mode.
4. The monitoring device according to any one of the claims 1 to 3, characterized by
   a use for monitoring the insulation resistance (Rf) for an ungrounded power converter system.
5. A monitoring device (103) for monitoring an insulation resistance (Rf) for an ungrounded electric system (2) which comprises a liquid cooling which is operated to ground using a refrigerant (3) and comprises a supply line (6) and a return line (8), the supply line (6) and the return line (8) each being realized as an electrically conductive tube section (10) which is connected to a ground potential (PE) and to which an electrically insulated tube section (12) is connected which has a tube length (l_i) and is connected to the electric system (2),
   characterized by

   a low-impedance measuring signal source (30) configured for generating a measuring signal having a measuring voltage (U_m), the measuring signal source (30) comprising a ground-potential connection (31) connected to the electrically conductive tube section (10) and comprising a coupling connection (32),

   a voltage meter (70) for measuring a partial voltage (U_i), the voltage meter (70) comprising a first voltage-meter input (72) connected to the coupling connection (32) of the measuring signal source (30), and the voltage meter comprising a second voltage-meter input (74),

   a conductive coupling tube element (50) which contacts the refrigerant (3) and is electrically connected to the coupling connection (32) of the measuring signal source (30) for synchronously coupling the measuring signal into the supply line (6) and the return line (8) in common mode,

   a conductive voltage-meter tube element (76) which contacts the refrigerant (3) and is connected to the second voltage-meter input (74) of the voltage meter (70),

   the coupling tube element (50) being disposed in such a manner on the electrically insulated tube section (12) that a coupling length (l_AK1) is yielded between the system-sided end of the electrically conductive tube section (10) and the coupling tube element (50), and the voltage-meter tube element (76) being disposed in such a manner adjacent to the electrically insulated tube section (12) that a voltage-meter length (l_AK2) is yielded between the coupling tube element (50) and the voltage-meter tube element (76) and a resistance length (l_Ri) is yielded between the voltage-meter tube element and the electric system,

   a computing unit which is configured for computing the insulation resistance from the measuring voltage (U_m) of the measuring signal, a supplied measuring current (I_m), the partial voltage (U_i), the coupling length (l_AK1), the voltage-meter length (l_AK2) and the resistance length (l_Ri).
6. The monitoring device according to claim 5,
   characterized by
   a use for monitoring the insulation resistance (Rf) for an ungrounded power converter system.
7. An enhanced monitoring device (110) for monitoring a shared insulation resistance (R_f) of several ungrounded electric subsystems (16) which are fed by a shared transformer (15) and each comprise a liquid cooling operated to ground using a refrigerant (3) and comprising a supply line (6) and a return line (8), the supply line (6) and the return line (8) each being realized as an electrically conductive tube section (10) which is connected to a ground potential (PE) and to which an electrically insulated tube section (12) is connected which has a tube length (l_i) is and connected to the corresponding electric subsystem (16),
   characterized in that

   at least two of the electric subsystems (16) are equipped with a monitoring device (100, 101, 102, 103) according to any one of the claims 1 to 6, and

   a synchronization control device (80) for synchronously coupling the measuring signals into the electric subsystems (16) to be monitored is installed.
8. The enhanced monitoring device (110) according to claim 7, characterized in that
   the synchronization control device (80) comprises an amplitude control device (82) for controlling the measuring-signal amplitudes of the measuring signals generated in the corresponding monitoring devices (100, 101, 102, 103).
9. A method for monitoring an insulation resistance (Rf) for an ungrounded electrical system (2) which comprises a liquid cooling which is operated to ground using a refrigerant (3) and comprises a supply line (6) and a return line (8), the supply line (6) and the return line (8) each being realized as an electrically conductive tube section (10) which is connected to a ground potential (PE) and to which an electrically insulated tube section (12) is connected which is connected to the electric system (2) and has a tube length (l_i), the method comprising the steps:

   generating a measuring signal having a measuring voltage (U_m) using a low-impedance measuring signal source (30),

   synchronously coupling the measuring voltage (U_m) in common mode into the supply line (6) and the return line (8) having a conductive coupling tube element (50) contacted with the refrigerant (3),

   measuring a coupling current (I_AK) which flows in the refrigerant (3), which flows through the electrically insulated tube section (12), using a coupling-current measuring sensor (40), measuring a fault current (I_Ri) which flows in the refrigerant (3), which flows through the electrically insulated tube section (12), using a fault-current measuring sensor (42) switched downstream of the coupling-current measuring sensor (40) in the direction of the electric system (2),

   the coupling tube element (50) being disposed in such a manner on the electrically insulated tube section (12) between the coupling-current measuring sensor (40) and the fault-current measuring sensor (42) that the tube length (l_i) of the electrically insulated tube section (12) is divided into a coupling length (I_AK) extending between the electrically conductive tube section (10) and the coupling tube element (50) and a resistance length (l_Ri) extending from the coupling tube element (50) to the electric system (2), computing the insulation resistance (Rf) from the measuring voltage (U_m) of the measuring signal, the detected coupling current (I_AK), the detected fault current (I_Ri), the coupling length (I_AK) and the resistance length (l_Ri) using a computing unit (60).
10. The monitoring method according to claim 9,
    characterized by
    a use for monitoring the insulation resistance (Rf) for an ungrounded power converter system.
11. A method for monitoring an insulation resistance (Rf) for an ungrounded electric system (2) which comprises a liquid cooling which is operated to ground using a refrigerant (3) and comprises a supply line (6) and a return line (8), the supply line (6) and the return line (8) each being realized as an electrically conductive tube section (10) which is connected to a ground potential (PE) and to which an electrically insulated tube section (12) is connected which is connected to the electric system (2) and has a tube length (l_i), the method comprising the steps:

    generating a measuring signal having a measuring voltage (U_m) via a measuring signal source (30) which comprises a ground-potential connection (31), which is connected to the electrically conductive tube section (10), and a coupling connection (32),

    synchronously coupling the measuring voltage (U_m) in common mode into the supply line (6) and the return line (8) having a conductive coupling tube element (50) which is contacted with the refrigerant (3) and is electrically connected to the coupling connection (32) of the measuring signal source (30),

    measuring a partial voltage (Ui) using a voltage meter (70) which comprises a first voltage-meter input (72) connected to the coupling connection (32) of the measuring signal source (30) and a second voltage-meter input (74) connected to a conductive voltage-meter tube element (76) contacted with the refrigerant (3),

    the coupling tube element (50) being disposed in such a manner on the electrically insulated tube section (12) that a coupling length (l_AK1) is yielded between the electrically conductive tube section (10) and the coupling tube element (50), and the voltage-meter tube element (76) is adjacently disposed in such a manner on the electrically insulated tube section (12) that a voltage-meter length (l_AK2) is yielded between the coupling tube element (50) and the voltage-meter tube element (76) and a resistance length (l_Ri) is yielded between the voltage-meter tube element (76) and the electric system (2),

    computing the insulation resistance (Rf) from the measuring voltage (U_m) of the measuring signal, a supplied measuring current (I_m), the partial voltage (U_i), the coupling length (l_AK1), the voltage-meter length (l_AK2) and the resistance length (l_Ri).
12. The monitoring method according to claim 11,
    characterized by
    a use for monitoring the insulation resistance (Rf) for an ungrounded power converter system.
13. An enhanced method for monitoring a shared insulation resistance of several ungrounded electric subsystems (16) which are fed by a shared transformer (15) and each comprise a liquid cooling which is operated to ground using a refrigerant (3) and comprises a supply line (6) and a return line (8), the supply line (6) and the return line (8) each being realized as an electrically conductive tube section (10) which is connected to a ground potential (PE) and to which an electrically insulated tube section (12) is connected which is connected to the corresponding electric subsystem (16) and has a tube length (l_i),
    characterized in that
    at least two of the ungrounded electric subsystems (16) are monitored using a method for monitoring an insulation resistance according to any one of the claims 9 to 12 and the measuring signals are synchronously coupled into the electric subsystems (16) to be monitored by means of a synchronization control device (18).
14. The enhanced monitoring method according to claim 13, characterized in that
    the measuring-signal amplitudes of the measuring signals are controlled by means of an amplitude control device (82).

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